The present invention relates generally to compression fittings for coupling the end of a length of tubing to another member, and more particularly to such a fitting which is of a ferruled-variety and which is particularly adapted for use with hardened or other tubing used in “medium” pressure applications.
Compression fittings of a ferruled-type are widely employed in a variety of instrumentation, pneumatic, hydraulic, process, power, refrigeration, and other fluid transport applications utilizing plastic or metal tubing. Typically employing one or two ferrules for gripping the tubing and forming a fluid-tight seal between the tubing and the fitting body, these fittings have been adapted for use as connectors with many different tubing types including plastics such as polyurethane (PU), polytetrafluoroethylene (PTFE), fluorinate ethylene polypropylene (FEP), perfluoroalkoxy resin (PFA), polyethylene (PE), polypropylene (PP), rigid and flexible nylon, acrylonitrile-butadiene-styrene (ABS) copolymer, and metals such as copper, brass, steel, stainless steel, titanium, aluminum, and alloys such as nickel-copper, Hastelloy®, Alloy 600, 6Mo, Inconel®, Incoloy®, and the like.
In basic construction, such fittings for use with metal tubing generally are formed from the same metal as the tubing (or in the case of copper tubing from brass) as including a body and one or more branches, ends, or other openings for connection to a tubing end. Often, these fittings are termed as being standard or inverted depending on the style of nut which is used in the fitting. Under such convention, “standard” nuts are internally-threaded for engagement with an externally-threaded body, with “inverted” nuts being externally-threaded threaded for engagement with an internally-threaded body. Tube fittings of the type herein involved are manufactured by the Instrumentation Connectors Division of Parker-Hannifin Corp., Huntsville, Ala., and are sold commercially under the tradename A-Lok® and CPI™. Other representative tube fittings of the type herein involved are described in U.S. Pat. Nos. 2,484,815; 2,749,152; 3,075,793; 3,103,373; 3,215,457; 3,402,949; 3,445,128; 3,499,671; 3,584,900; 3,695,647; 3,722,923; 4,076,286; 4,776,618; 4,826,218; 4,915,427; 4,940,263; 5,074,599; 5,351,998; 5,882,050; and 5,934,714.
A representative tube fitting of the above-mentioned inverted style is shown generally at 10 in FIG. 1 which is labeled “prior art.” Such fitting 10 includes a body, 12, having an external surface, 14, and an internal bore, 16. Bore 16 extends coaxially with a central longitudinal axis, 18, which for convenience in the discourse to follow is transposed at 18′. Depending upon the configuration of the fitting 10, the body external surface 14 may be configured as having hexagonal or other flats portions for engagement with a wrench or other tool during make-up or disassembly. Also, and again as depending upon the configuration of the fitting 10, body 12 may extend in a “straight” configuration, such as for a union or a reducer or other adapter, along axis 18 intermediate a rearward end or port, 20, which may be configured in the manner to be described for a tubing connection, and a forward end, 22, which, although not shown as such, similarly may be configured for another tubing connection. Of course, and as is known, by providing body 12 as having ends or branches which are angled, or as having multiple ends or branches, configurations other than straight, such as elbows, tees, or crosses may be provided. Forward end 22 also may be configured instead for a male or female pipe, welded, or other connection. Alternatively, body 12 itself may be a manifold, valve, piston, or other component or structure. In the disclosure to follow, the axial directions along axis 18 will be referred to as “forward,” “forwardly,” or “front” if in the axial direction of the body forward end 22, and as “rearward,” “rearwardly,” or “rear” if in the counter axial direction of the body rearward end 20.
In the embodiment 10 of FIG. 1, bore 16, which has an inner circumferential surface, 24, is counterbored beginning from the body rearward end 20 and extends forwardly therefrom along axis 18 into body 12 in a stepwise fashion of generally decreasing diametric extent in defining a rearward opening, 26, an annular seating surface, 28, and a generally cylindrical tube support portion, 30. Opening 26, which is internally-threaded as shown at 31, is sized to accept a distal end, 32, of a length of tubing, 34, as such tubing end 32 is received coaxially through generally annular front and rear ferrules, 36 and 38, respectively, which may be preset onto the tubing outer diameter in a manner known in the art, and a generally annular, “inverted” nut, 40, having a generally cylindrical inner surface, 41. Seating surface 28 is sized for an abutting engagement with the front ferrule 36, and is configured as having a generally frustoconical geometry which is inclined in the rearward direction along axis 18 to define a given angle, referenced at θ1, of typically about 20° as measured relative to axis 18 and/or the bore inner surface 24, and as having a given axial length, referenced at “l.” Tube support portion 30, in turn, is sized to receive the tubing end 32 and in that regard has an inner diameter which is marginally larger than the tubing 34 outer diameter for a close tolerance fit therewith. The travel of tubing end 32 into the bore 16 may be delimited by a positive axial stop provided by the abutting engagement of the tubing end 32 against a rearward-facing wall, 43, of a generally-annular internal shoulder defined by the forward terminus of the tube support portion 30.
Ferrules 36 and 38 are provided to compressively grip or “bite” the tubing 34 outer diameter both for retaining the tubing end 32 within the body 12 and for effecting a fluid-tight seal therebetween. Each of the ferrules 36 and 38 extends intermediate a forward end or nose, 44 and 46, respectively, and a rearward end, 48 and 50, respectively, and has a generally cylindrical inner surface, 52 and 54, respectively. A forward outer surface, 56 and 58, respectively, extends rearwardly from the corresponding nose 44 or 46, and is configured as having a generally frustoconical geometry which is inclined in the rearward direction along axis 18 to define a given included angle, referenced respectively at α1 and α2, with the axis 18 and/or the corresponding inner surface 52 or 54 of typically about 15° for α1, and between about 35-45° for α2. The forward outer surface 56 of the front ferrule 36 thereby defines a differential angle of about 5° with the confronting body seating surface 28 such that a camming action is developed as the front ferrule 36 is urged into abutting engagement against the seating surface 28 during the makeup of the fitting 10. Similarly, the forward outer surface 58 of the rear ferrule 38 defines a differential angle of from about 1-10° with a confronting seating surface, 60, formed in the front ferrule rearward end 48 as extending generally from the ferrule inner surface 52. Further in this regard, seating surface 60 is configured as having a generally frustoconical geometry which is rearwardly inclined to define a given included angle, referenced at θ2, with the axis 18 of typically about 45°.
The rearward end 50 of the rear ferrule 38 also has a generally frustoconical geometry, but as inclined in the forward direction along axis 18 in defining an included angle, referenced at β, of about 75°, with the ferrule inner surface 54 and/or the axis 18. During the makeup of the fitting 10, such end 50 is abutting engageable in an axial force transferring contact with a generally frustoconical thrust surface, 62, formed at the forward end, 63, of nut 40. Typically, the thrust surface 62, which is also forwardly inclined is configured as the supplement of angle β, and in this regard defines an included angle, referenced at δ, of about 105° with the nut inner surface 41 and/or axis 18. Nut 40 further is configured as having a having forward portion, 64, which is externally-threaded as shown at 66, and a rearward portion, 68, which may be configured as having hexagonal or other flats for engagement with a wrench or other make-up tool.
In the makeup of the fitting 10, with the tubing end 32 received coaxially through, in series, nut 40, rear ferrule 38, and front ferrule 36, and with the ferrules 36 and 38 optionally preset thereon, the tubing end 32 and ferrules 36 and 38 may be received through the opening 26 and into bore 16, with the advancement thereof being delimited by the abutting engagement of the tubing end 32 against the shoulder wall 43 of the body tube support portion 30. Thereupon, the external threads 66 of the nut forward portion 64 may be threadably rotatably engaged with the internal threads 31 of the body opening 26 urging, by means of the tightening of the nut 40 and the concomitant axial force transferring contact of the nut thrust surface 62 against the rear ferrule rearward end 50, the rear ferrule forward outer surface 58 into a camming engagement with the confronting seating surface 60 of the front ferrule rearward end 48 and, in turn, the front ferrule forward outer surface 56 into camming engagement with the confronting body seating surface 28. As the tightening of the nut 40 progresses, such as to a specified torque, displacement, or rotation setting, the ferrule noses 44 and 46 are compressed radially inwardly about the tubing outer diameter both to grippably retain the tubing end 32 in the fitting body 12 and to develop a fluid-tight, metal-to-metal seal between the front ferrule forward outer surface 56 and the body seating surface 28, and between one or both of the ferrule noses 44 and 46 and the outer diameter of the tubing 34. For improved gripping of the tubing, rear ferrule 38 may be surface or case hardened, such as to a Rockwell (Rc) hardness of at least about 50, by a chemical process such as nitriding, carburizing, case carburization, or Kolsterizing, or by a heat treatment or other heat treatment method such as precipitation hardening, work hardening, or a surface coating or plating.
As the use of tubing continues to increase for chemical process and other applications, it will be appreciated that improvements in tube fittings therefor would be well-received by industry. It is believed that there presently exists a need for a fitting for use with thicker walled, i.e., between about 0.062-0.21 inch (1.5-5 mm), and non-annealed, harder, i.e., at least about 20 Rc, tubing for use at “medium” working pressures of between about 10-15 Ksi (70-100 KPa). Although fittings are currently available which are specified for use in “medium” pressure applications, these fittings generally are of a “non-standard” variety in requiring additional components or makeup steps. Accordingly, it is believed that particularly desired would be a fitting which employs standard componentry and which may be made or disassembled in a conventional fashion so as to have a familiarity to technicians and other involved in the installation or maintenance of the tubing system.
In this regard, however, fittings of a conventional design which are currently used with softer, annealed tubing used in instrumentation and other applications at lower operating pressure of up to about 10 Ksi (70 KPa), cannot simply be resized for use with tubing which may be as hard as the ferrules of the fitting itself For example, reference may be had to FIG. 2 wherein fitting 10 of FIG. 1 reappears at 10′ as made up with “medium” pressure tubing which is designated at 34′. As may be seen, the use of a fitting designed for softer, annealed tubing with harder tubing can result in a condition wherein the ferrules 36 and 38, rather than being cammingly compressed in a controlled fashion about the tubing outer diameter, instead are caused to flare outwardly with, particularly, the end 48 of the front ferrule 36 being expanded to an outer diameter which could interfere with the body internal threads 31 and thereby delimit the removal of the tubing end 32′ from the body 12 during disassembly. Thus, a preferred fitting for medium pressure tubing would allow for a conventional makeup and disassembly, as for fitting 10, but also would be specially design for such tubing in minimizing the potential for ferrule flaring or other assembly problems.